241 



3. Account of a peculiar Structure found in the Vagmarus 



Islandicus. By Dr John Reid. Communicated by Pro- 

 fessor Goodsir. 



4. Notes to a Paper on the Motive Power of Heat. By Pro- 



fessor William Thomson. 



(1.) On the Values of /i derived from Observations on the Vapours 

 of various Liquids. 

 An important test of the truth of the axiom on which Carnot's 

 Theory is founded, will be afforded by comparing the values of /j, 

 deduced from observations on various liquids. I am informed by 

 Mons. Regnault, that, by the end of this year, data as complete as 

 those whidi we at present possess for water, will be supplied for five 

 or six different liquids, from certain investigations with which he is 

 now occupied. Carnot gives values of ^ for the temperatures of the 

 boiling of sulphuric ether, alcohol, water, and essence of turpentme, 

 derived from various observations upon those liquids. The compari- 

 son of these with the values of /x, deduced from Regnaulfs continu- 

 ous series of observations on water, are exhibited in the following 

 table : — 



The coincidences of the results obtained by such very different* 

 experiments are very striking. The differences certainly lie within 

 the limits of the errors of observation ; for it happens that the dif- 

 ference of the two results deduced by the different experimenters, 

 from water at the boiling-point, is greater than any of the other 

 differences. It is very remarkable that the feature of the gradual 



